This invention relates to an apparatus for heating printed circuit boards which is comprised of a conveyor to transport printed circuit boards, and a heating chamber through which the printed circuit boards on the conveyor pass.
In this type of apparatus, there is for example a reflow soldering apparatus. In this reflow soldering apparatus, printed circuit boards mounted with electronic components are heated in a heating chamber filled for example with an inert gas, while being transported by a conveyor, and the solder paste melts and the electronic components are soldered. In the apparatus of the conventional art, heat insulating material such as glass wool is installed on the surrounding wall of the heating chamber for a high temperature in the heating chamber, and the heat is kept within the heating chamber by means of this type of heat insulating material.
In this type of apparatus, however, the heating chamber is required to achieve high temperatures with a heater, so that along with consuming as little electrical power of the heater as possible and having energy-saving features, a design with low running costs is needed.
However, since the apparatus of the conventional art uses a heat insulating material such as glass wool for heat insulation in the heating chamber, there is a limit to the degree of obtainable heat insulation. When the glass wool is made thicker to improve the heat insulation, the dimensions around the heating chamber become larger, leading to the problem of an apparatus of increased size and weight. Therefore, using the apparatus of the conventional art requires increasing the amount of electrical power to the heater in order to compensate for lowering of heating chamber temperatures, the electrical power consumption of the heater increases, and along with the problem of poor energy-saving, also brings about the problem of high running costs due to the high electrical fees.
This type of apparatus also needs a design of course capable of insulating the heating chamber, yet producing as little industrial waste as possible when disposal of the apparatus is required, in view of the need for protecting the environment and reducing the amount of rubbish.
The apparatus of the conventional art uses a heat insulating material such as glass wool and this type of heat insulating material is normally used in a thickness of 3 to 4 centimeters on the surrounding wall of the heating chamber. Accordingly, large quantities of heat insulating material are used in the apparatus of the conventional art, causing the unavoidable problem that large quantities of industrial waste are generated by this heat insulating material becoming trash when disposal of the apparatus is required.
This invention therefore has the object of providing an apparatus for heating a printed circuit board which is capable of reducing electrical power consumption of the heater due to good heat insulation, and also reducing amount of industrial waste.
An apparatus for heating a printed circuit board of this invention comprises a conveyor to transport a printed circuit board, and a heating chamber through which the printed circuit board on the conveyor passes, wherein a vacuum layer for heat insulation is formed in a surrounding wall of the heating chamber.
The printed circuit board includes not only a board in which a conductor is fixed to the board, but also a board in which electronic components are mounted on the board having a conductor fixed. A drying device and a soldering apparatus are for example present in the apparatus for heating a printed circuit board.
The vacuum layer for heat insulation is preferably formed to cover the entire circumferential area of the heating chamber, however forming the vacuum layer on just the desired sections is permissible.
A rib for reinforcing the surrounding wall is preferably secured to the surrounding wall in order to prevent warping of the surrounding wall. The reinforcing rib preferably has a cross section with a T-shape, an I-shape, a channel shape, an inverted L-shape or a rectangular shape. Manufacture of any of the above type of rib is easy, and increased strength in the surrounding wall can be obtained in the simple structure. The reinforcing rib is provided on at least one of the outer circumferential surface of the surrounding wall and the inner circumferential surface facing the heating chamber. The reinforcing rib is also preferably provided on the periphery of the surrounding wall at a surface perpendicular to the direction of conveyor transport for increased strength.
This invention is further preferably installed with a member in the vacuum layer to prevent collapse of the surrounding wall. The surrounding wall can be hardened even further by insertion of this member. Preferably, at least a portion of this member is formed of heat insulation material to prevent heat conduction. Preferably, as small an area as possible is selected for the area where the member contacts the surrounding wall in order to suppress heat conduction. When the vacuum layer is formed in separate compartments by means of the above member, then each compartment is preferably communicated with each other.
This invention is preferably installed with a member in the vacuum layer to intercept radiant heat. A high heat insulating effect is obtained when such a member is installed because the radiant heat is intercepted. White cotton, glass fibers or gypsum, etc. may be utilized as the material for intercepting the radiant heat. If a radiant heat reflective member such as aluminum foil or silver paper is placed over the radiant heat intercepting member, an ever higher heat insulating effect can be obtained.
A reflective layer for radiant heat is preferably provided on the surface of the surrounding wall facing the heating chamber. Installing this reflective layer further prevents radiant heat from escaping outside the heating chamber.
A vacuum pump is preferably connected to the vacuum layer in the surrounding wall to allow evacuating the vacuum layer. If there is a drop in the vacuum level in the vacuum layer in the surrounding wall, a vacuum pump allows constantly maintaining the vacuum level in the vacuum layer in the surrounding wall at a specified level.
The heating chamber of this invention further preferably comprises a preheating chamber for preheating the printed circuit board, a reflow soldering chamber for melting the solder paste and soldering the electronic components on the printed circuit board, arranged in order, along the direction of transport by the conveyor. In such cases, the heating chamber for the reflow soldering apparatus can be heat insulated by vacuum. When a plurality of heating chambers are used, then a vacuum layer may be formed only for the desired heating chamber.